Recently, many studies have been in progress so as to support high-quality and high-speed data transmission in a radio communication environment. Among them, the OFDM uses limited frequencies efficiently to be used for a broadcasting system such as a digital video broadcasting-terrestrial and handheld (DVB-T/H) and a digital multimedia broadcasting (DMB), and it is an influential candidate for fourth-generation communication and next generation broadcasting.
A transmitting end of a communication system using the OFDM scheme modulates serial data symbols, demultiplexes the same into parallel data, and performs an inverse fast Fourier transform (IFFT) on the same. The transmitting end allocates a plurality of subcarriers to the demultiplexed parallel data, and then transmits resultant data to a receiving end. The receiving end performs a fast Fourier transform (referred to as FFT hereinafter) on the received signal to separate a subcarrier from the received signal, multiplexes the parallel data from which the subcarrier is separated into serial data, and demodulates the multiplexed serial data to detect a desired data symbol.
In this instance, FFT output data from the OFDM transmitting end generates inter-carrier interference (referred to as ICI hereinafter) according to a radio channel characteristic. Before the OFDM receiver performs an FFT, it may suppress inter-carrier interference and reduce a noise component by using an area where there is no OFDM inter-symbol interference (referred to as ISI hereinafter).
That is, when the FFT input data for performing an FFT operation is configured, sample data of the guard interval (GI) without ISI in the time domain, that is, the symbol interference free interval and sample data of the effective symbol interval, are summed. An FFT operation on the FFT input data including the summed sample data is performed. Korean Patent Application Publication 2010-0039467 discloses content for reducing ICI and a noise component through an FFT operation.
In this instance, when the sample data of the symbol interference free interval and the sample data of the effective symbol interval are summed and in the case of a Frank window, they may be added by using a ratio of the FFT side vs. the symbol interference free interval.
In the case of another existing case, a method for taking an average by setting respective weight values that correspond to 0.5 can be used. That is, the weight value of 0.5 is respectively provided to the sample data of the symbol interference free interval and the sample data of the effective symbol interval, and the average thereof is calculated. This method is similar to equal gain combining (referred to as EGC hereinafter). Here, the EGC signifies phase-coherent combining of different channels with a substantially equivalent weight value.
However, if the channels are abruptly changed by a mobile environment, a signal-to-noise ratio (referred to as SNR hereinafter) of the symbol interference free interval may be higher or lower than an SNR of the effective symbol interval.
FIG. 1 shows a conventional OFDM symbol.
Referring to FIG. 1, a change width of channel power of a guard interval and an effective symbol interval is large.
As described, when the channel change is large and a simple summation of the sample data of the symbol interference free interval and the sample data of the effective symbol interval is performed in a like manner of prior art, a problem that the SNR fails to obtain a gain of a large interval is generated.